U.S. patent number 5,852,997 [Application Number 08/859,158] was granted by the patent office on 1998-12-29 for common rail injector.
This patent grant is currently assigned to Stanadyne Automotive Corp.. Invention is credited to Richard E. Vanderpoel.
United States Patent |
5,852,997 |
Vanderpoel |
December 29, 1998 |
**Please see images for:
( Certificate of Correction ) ** |
Common rail injector
Abstract
An injector for a common rail fuel injection system employs a
solenoid operated valve configuration which functions to control
the amount of filling by regulating the start of filling and the
end of filling between the injection events. In some embodiments, a
three-way solenoid valve is employed. The start of injection is
controlled by a control piston. An intensifier piston is employed
to increase the injection pressure. A pilot piston assembly may
also be employed to regulate the shape of the injection.
Inventors: |
Vanderpoel; Richard E.
(Bloomfield, CT) |
Assignee: |
Stanadyne Automotive Corp.
(Windsor, CT)
|
Family
ID: |
25330207 |
Appl.
No.: |
08/859,158 |
Filed: |
May 20, 1997 |
Current U.S.
Class: |
123/446; 123/300;
123/456 |
Current CPC
Class: |
F02M
63/0225 (20130101); F02M 57/025 (20130101); F02M
57/026 (20130101); F02M 45/04 (20130101); F02M
59/105 (20130101) |
Current International
Class: |
F02M
59/10 (20060101); F02M 57/00 (20060101); F02M
63/00 (20060101); F02M 57/02 (20060101); F02M
63/02 (20060101); F02M 59/00 (20060101); F02M
45/00 (20060101); F02M 45/04 (20060101); F02M
037/00 () |
Field of
Search: |
;123/446,456,300,299,447 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Miller; Carl S.
Attorney, Agent or Firm: Alix, Yale & Ristas, LLP
Claims
What is claimed is:
1. A fuel injector for a common rail injection system
comprising:
an injector body having axially spaced inlet and injection
portions, said injection portion defining an injection orifice, a
nozzle chamber and an interior valve seat, said inlet portion
comprising a rail inlet for receiving pressurized fuel supplied to
said injector;
an injector valve mounted in said body and engageable with said
seat to prevent fuel communication through said injection orifice
and during an injection event axially displaceable from said seat
for injecting pressurized fuel through said orifice;
a control unit comprising a control chamber and a control piston
axially displaceable in said control chamber;
a pump unit comprising a pump chamber and a pump piston axially
displaceable in said pump chamber;
a nozzle conduit connecting said pump chamber and said nozzle
chamber;
a control valve assembly comprising a control valve to provide
selective fuel communication between said rail inlet and said
control and pump chambers for controlling the supply of pressurized
fuel in said pump chamber and said control chamber, said pump
piston being displaced for the injection of pressurized fuel by
opening said control valve to vent pressure from said control
chamber,
so that fuel is controllably supplied to said pump chamber between
injection events and the fuel in said control chamber is
selectively controlled to start an injection whereby said injector
valve is displaced by pressurized fuel in said nozzle chamber to
inject pressurized fuel through said injection orifice.
2. The injector of claim 1 further comprising an intensifier unit
responsive to pressure supplied at said rail inlet and comprising
an intensifier chamber and an intensifier piston.
3. The injector of claim 2 wherein the pressure in the pump chamber
upon displacement of the pump piston during an injection pump
stroke is proportional to the rail pressure at said rail inlet.
4. The injector of claim 1 wherein said pump piston is displaced
for the injection of pressurized fuel by opening said control valve
to vent pressure from said control chamber.
5. The injector of claim 1 wherein said injector valve is biased to
the engaged position with said seat and said injector valve is
displaceable from said seat when pressure in said nozzle chamber
exceeds the biasing pressure of the injector valve.
6. The injector of claim 1 further comprising a pilot valve
assembly comprising a piston which is displaced to implement a
pilot injection during said injection event.
7. The injector of claim 1 wherein said control valve has a first
position wherein pressure in said control chamber is vented and a
second position wherein the control chamber is filled with
pressurized fuel.
8. The injector of claim 1 wherein said control valve comprises a
three-way valve having a first position wherein pressure in said
control chamber is vented, a second position wherein the control
chamber and pump chamber are supplied with pressured fuel and a
third position wherein communication of fuel to said pump chamber
is terminated.
9. The injector of claim 1 further comprising a solenoid for
controlling the position of said control valve.
10. The injector of claim 9 further comprising an electronic
control system for controlling the operation of said solenoid.
11. The injector of claim 1 further comprising a check valve
disposed between said control valve and said pump chamber.
12. The injector of claim 1 wherein said control valve is disposed
in a control valve chamber and further comprising a trim valve for
selectively controlling the rate of fuel supplied to said control
valve chamber.
13. The injector of claim 2 wherein said control piston,
intensifier piston and pump piston are axially displaced
substantially simultaneously to start the fuel injection event.
14. A fuel injector for a common rail injection system
comprising:
an injector body having axially spaced inlet and injection
portions, said injection portion defining an injection orifice, a
nozzle chamber and a valve seat, said inlet portion comprising a
rail inlet for receiving pressurized fuel supplied to said
injector;
an injector valve mounted in said body and engageable with said
seat to prevent fuel communication through said injection orifice
and during an injection event displaceable from said seat for
injecting pressurized fuel through said orifice;
a control unit disposed in said injector body comprising a control
chamber and a control piston displaceable in said control
chamber;
a pump unit comprising a pump chamber and a pump piston coupled to
said control piston displaceable in said pump chamber to define an
injection pump stroke;
a control valve assembly comprising at least one control valve
disposed in fluid communication relationship between said rail
inlet and said control and pump chambers for selectively
controlling the supply of pressurized fuel in said pump chamber and
said control chamber,
so that fuel is controllably supplied to said pump chamber between
injection events and the fuel pressure in said control chamber is
vented by said control valve to start an injection whereby said
injector valve is displaced by pressurized fuel produced by said
pump stroke to inject pressurized fuel through said injection
orifice.
15. The injector of claim 14 further comprising a third unit
responsive to pressure supplied at said rail inlet and comprising a
third chamber and a third piston engageable with said control
piston.
16. The injector of claim 15 wherein the pressure in the pump
chamber during the injection pump stroke is greater than the rail
pressure at said rail inlet.
17. The injector of claim 2 wherein said pump piston is displaced
for the injection of pressurized fuel by opening said control valve
to vent pressure from said control chamber.
18. The injector of claim 14 further comprising a solenoid for
controlling the position of one of said at least one control
valve.
19. A fuel injector for a common rail injection system
comprising:
an injector body having a rail inlet for receiving pressurized fuel
supplied to said injector and an injection portion, said injection
portion defining an injection orifice, a nozzle chamber and an
interior valve seat;
an injector valve mounted in said body and engageable with said
seat to prevent fuel communication through said injection orifice
and during an injection event displaceable from said seat for
injecting pressurized fuel through said orifice;
a control unit comprising a control chamber and a control piston
displaceable in said control chamber;
a pump unit comprising a pump chamber and a pump piston
displaceable in said pump chamber;
nozzle conduit means for fluidly connecting said pump chamber and
said nozzle chamber;
a control valve assembly comprising a control valve which
selectively controls fluid communication between said rail inlet
and said control and pump chambers for selectively controlling the
supply of pressurized fuel in said pump chamber and said control
chamber,
a solenoid for operating said control valve;
so that fuel is controllably supplied to said pump chamber between
injection events and the pressure of fuel in said control chamber
is selectively vented to start the injection whereby said injector
valve is displaced by pressurized fuel in said nozzle chamber to
inject pressurized fuel through said injection orifice.
20. The injector of claim 19 further comprising a third unit
responsive to pressure supplied at said rail inlet and comprising a
third chamber and a third piston, said pump piston being coupled to
said control piston, said control piston and said third pistons
being engageable.
21. A fuel injector for a common rail injection system
comprising:
an injector body having axially spaced inlet and injection
portions, said injection portion defining an injection orifice, a
nozzle chamber and an interior valve seat, said inlet portion
comprising a rail inlet for receiving pressurized fuel supplied to
said injector;
an injector valve mounted in said body and engageable with said
seat to prevent fuel communication through said injection orifice
and during an injection event axially displaceable from said seat
for injecting pressurized fuel through said orifice;
a control unit comprising a control chamber and a control piston
axially displaceable in said control chamber;
a pump unit comprising a pump chamber and a pump piston axially
displaceable in said pump chamber;
a nozzle conduit connecting said pump chamber and said nozzle
chamber;
a control valve assembly comprising a control valve to provide
selective fuel communication between said rail inlet and said
control and pump chambers for controlling the supply of pressurized
fuel in said pump chamber and said control chamber, said control
valve comprising a three-way valve having a first position wherein
pressure in said control chamber is vented, a second position
wherein the control chamber and pump chamber is supplied with
pressurized fuel and a third position wherein communication of fuel
to said pump chamber is terminated,
so that fuel is controllably supplied to said pump chamber between
injection events and the fuel in said control chamber is
selectively controlled to start an injection whereby said injector
valve is displaced by pressurized fuel in said nozzle chamber to
inject pressurized fuel through said injection orifice.
22. A fuel injector for a common rail injection system
comprising:
an injector body having axially spaced inlet and injection
portions, said injection portion defining an injection orifice, a
nozzle chamber and an interior valve seat, said inlet portion
comprising a rail inlet for receiving pressurized fuel supplied to
said injector;
an injector valve mounted in said body and engageable with said
seat to prevent fuel communication through said injection orifice
and during an injection event axially displaceable from said seat
for injecting pressurized fuel through said orifice;
a control unit comprising a control chamber and a control piston
axially displaceable in said control chamber;
a pump unit comprising a pump chamber and a pump piston axially
displaceable in said pump chamber;
a nozzle conduit connecting said pump chamber and said nozzle
chamber;
a control valve assembly comprising a control valve chamber and a
control valve to provide selective fuel communication between said
rail inlet and said control and pump chambers for controlling the
supply of pressurized fuel in said pump chamber and said control
chamber; and
a trim valve for selectively controlling the rate of fuel supplied
to said control valve chamber,
so that fuel is controllably supplied to said pump chamber between
injection events and the fuel in said control chamber is
selectively controlled to start an injection whereby said injector
valve is displaced by pressurized fuel in said nozzle chamber to
inject pressurized fuel through said injection orifice.
23. A fuel injector for a common rail injection system
comprising:
an injector body having axially spaced inlet and injection
portions, said injection portion defining an injection orifice, a
nozzle chamber and a valve seat, said inlet portion comprising a
rail inlet for receiving pressurized fuel supplied to said
injector;
an injector valve mounted in said body and engageable with said
seat to prevent fuel communication through said injection orifice
and during an injection event displaceable from said seat for
injecting pressurized fuel through said orifice;
a control unit disposed in said injector body comprising a control
chamber and a control piston displaceable in said control
chamber;
a pump unit comprising a pump chamber and a pump piston coupled to
said control piston displaceable in said pump chamber to define an
injection pump stroke;
a third unit responsive to pressure supplied at said rail inlet
comprising a third chamber and a third piston engageable with said
control piston;
a control valve assembly comprising at least one control valve
disposed in fluid communication relationship between said rail
inlet and said control and pump chambers for selectively
controlling the supply of pressurized fuel in said pump chamber and
said control chamber, said pump piston being displaced for the
injection of pressurized fuel by opening said control valve to vent
pressurized fuel from said control chamber,
so that fuel is controllably supplied to said pump chamber between
injection events and the fuel pressure in said control chamber is
selectively controlled to start an injection whereby said injector
valve is displaced by pressurized fuel produced by said pump stroke
to inject pressurized fuel through said injection orifice.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to injectors employed in fuel
injection systems for internal combustion engines. More
particularly, this invention relates to injectors employed in
common rail type fuel injection systems.
In common rail injection systems, multiple injectors are connected
to a source of pressurized fuel which is maintained at a common
pressure by an accumulator. The common rail pressure is modified to
control a valve for injecting pressurized fuel charges through the
injector into the engine cylinders. A number of injector
configurations have been advanced for common rail injection
systems.
One type of common rail injector controls the fuel quantity
injected through the injector orifice by starting and stopping the
high pressure fuel stream. This is typically accomplished by a
solenoid. The solenoid response time must be extremely fast,
typically on the order of 200 microseconds or less. Consequently,
the solenoid must be relatively sophisticated to ensure
repeatability and insensitivity to pressure variations.
Another type of injector is an accumulator injector. The
accumulator injector is operated on a principle wherein the
injector is filled for a relatively long duration. When a
pre-established pressure is achieved, a solenoid valve is activated
to allow fuel to be injected into the engine cylinder. One of the
deficiencies commonly exhibited by accumulator injectors is that
the rate shape characteristics of the injection can be undesirable.
In addition, for accumulator injectors, the opening pressure is
interrelated to the quantity of fuel injected. The accumulator
injector, however, does not require a high performance
solenoid.
Other injectors which have been advanced employ a hydraulic valve
control which is more readily adaptable to implementing a pilot
injection. These hydraulic valve control devices result in a
relatively high return flow to the fuel injection system and may
involve relatively complex control valve configurations. Some
injectors have employed intensifiers to intensify the pressure
within the nozzle. Such injectors allow for a lower rail pressure
but produce a relatively high return flow and have limited pilot
potential and relatively high actuator response requirements.
Reliability of injectors for common rail systems is extremely
important since injector failure has the potential to destroy the
internal combustion engine. Typically, the injectors connect to a
rail having pressures of 20,000 psi or more. These injectors are
typically operated with solenoid controls. A stuck valve, broken
tip or a malfunctioning of the electronics or the driver for the
solenoid valve can result in a sufficient quantity of fuel being
delivered to the cylinder to cause engine failure. Operational
compensation for structural and mechanical failures is highly
problematical since the time between detection of a problem and the
time when corrective action is required may be extremely short or
nonexistent. In accordance with general design principles, simpler
injector configurations may reduce the failure rate for the
injector but represent a tradeoff in performance requirements.
The present invention is designed to overcome some of the noted
deficiencies of prior injectors to provide improved injection
control which does not require a high performance solenoid to
obtain suitable operation in a common rail fuel injection
system.
SUMMARY OF THE INVENTION
Briefly stated, the invention in a preferred form is a fuel
injector for a common rail fuel injection system. The injector may
incorporate any of a number of solenoid operated control valve
configurations. The injector comprises an injector body having an
injection orifice, an interior nozzle chamber and an interior valve
seat. An injector valve is mounted in the body and engageable with
the seat to prevent fluid communication through the injection
orifice. During an injection event, the injector valve axially
lifts from the seat for injecting pressurized fuel through the
orifice.
A control piston is axially displaceable in a control chamber. A
pump piston coupled to the control piston is also axially
displaceable in a pump chamber. A nozzle conduit connects the pump
chamber and the nozzle chamber. Pressurized fuel supplied to the
injector is received at a rail inlet. A control valve assembly
which comprises a control valve is disposed in fluid communication
relationship between the rail inlet and the control and pump
chambers. The control valve selectively controls the supply of
pressured fuel to the pump chamber and the control chamber. Fuel is
supplied to the pump chamber between injection events, and the fuel
quantity is selectively controlled. The fuel pressure in the
control chamber is also selectively controlled to start the
injection so that the injector valve is displaced by pressurized
fuel in the nozzle chamber to thereby inject the pressured fuel
through the injection orifice.
An intensifier unit may also be employed. The intensifier unit is
responsive to pressure supplied at the rail inlet and includes an
intensifier chamber and an intensifier piston engageable with the
control piston. The pressure in the pump chamber during the
injection pump stroke is greater than the rail pressure at the rail
inlet. The pump piston is displaced to define the injection pump
stroke by opening the control valve to vent pressure from the
control chamber. The injector valve may be biased to the engaged
position by hydraulic pressure, and the injector valve is
displaceable from the seat when pressure in the nozzle chamber
exceeds the biasing pressure of the injector valve. In one
embodiment, a pilot valve assembly comprises a piston which lifts
to implement a pilot injection.
In one embodiment, the control valve has a first position wherein
pressure in the control chamber is vented and a second position
wherein the control chamber is filled with pressurized fuel. In
another embodiment, the control valve may have a three-way position
wherein in the first position pressure in the control chamber is
vented, in the second position the control chamber and pump chamber
are filled with pressurized fuel and in the third position
communication of fuel to the pump chamber is terminated. Preferably
a solenoid operates the control valve. An electronic control system
controls the operation of the solenoid.
A check valve may be disposed between the control valve and the
pump chamber. In one embodiment, the control valve is disposed in a
control valve chamber, and a trim valve adjusts the flow rate of
the fuel supplied to the control valve chamber. The control piston,
intensifier piston and pump piston are axially displaced
substantially simultaneously to start the fuel injection event.
An object of the invention is to provide a new and improved
injector for a common rail fuel injection system.
Another object of the invention is to provide a new and improved
common rail injector which operates in a highly reliable manner and
has an efficient, cost-effective construction.
A further object of the invention is to provide a new and improved
common rail injector which is capable of controlling the fuel
injection in a precise and highly reliable manner.
Other objects and advantages of the invention will become apparent
from the drawings and the specification.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a common rail system employing an
injector in accordance with the present invention;
FIG. 2 is a sectional view, partly in schematic, of a common rail
injector in accordance with the present invention;
FIG. 3 is a cross-sectional view of the injector of FIG. 2 taken
along the line 3--3 thereof;
FIG. 4 is an enlarged fragmentary sectional view of a modified form
of the injector of FIG. 2 incorporating a pilot control
therein;
FIG. 5 is a schematic view of a third embodiment of a common rail
injector illustrating a single stage, one-way valve
configuration;
FIG. 6 is a schematic view of a fourth embodiment of a common rail
injector illustrating a single stage, three-way valve
configuration;
FIG. 7 is a schematic view of a fifth embodiment of a common rail
injector illustrating a two stage, one-way valve configuration;
FIG. 8 is a schematic view of a sixth embodiment of a common rail
injector illustrating a two stage, three-way valve
configuration;
FIG. 9 is a representative graph illustrating the injection rate
over time for the injector of FIG. 2; and
FIG. 10 is a graphical representation illustrating an injected fuel
quantity for the injector of FIG. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to the drawings, wherein like numerals represent
like parts throughout the several figures, a common rail injector
10 is illustrated in conjunction with a common rail fuel injection
system designated generally by the numeral 12. The injectors 10
function to inject pressurized charges of fuel into the cylinders
of an internal combustion engine (not illustrated) for sequential
combustion therein.
The common rail system employs a high pressure rail 14 which acts
as an accumulator. A high pressure supply pump 16 connects with the
fuel tank 18 via a fuel filter 20 for pressurizing fuel supplied to
the accumulator. The accumulator includes a pressure regulator 24
which connects via line 26 for returning fuel to the tank 18. Each
of the injectors connects via a fitting 22. A rail line 28 provides
fluid communication between the accumulator and each injector. A
return line 29 connects each injector to the return line 26. An
electronic control 30 controls the operation of a solenoid
associated with each injector to thereby control the operation of
the corresponding injector 10.
With reference to FIG. 2, the common rail injector 10 comprises a
tubular nozzle body 32 having a nozzle tip 34. The nozzle body
houses a nozzle valve unit 36 and a piston assembly 40 and receives
a control valve assembly 50, as will be further described below.
The upper inlet end of the nozzle body includes a header 38 which
houses the control valve assembly 50 and defines various
passageways for external and internal fuel communication. The
injector header 38 is preferably threaded to an interior upper end
of a tubular element of the nozzle body and sealed by an O-ring
52.
As will be described in detail below, the piston assembly 40 stores
the fuel to be injected and provides any intensifier function. The
intensifier ratio may be one, greater than one or less than one.
The control valves direct the flow of fuel to the piston assembly
40 and may comprise one or multiple stages. The first stage is
usually directly controlled by a solenoid. A second stage may be
driven by rail pressure or an intermediate pressure.
The header includes a transverse inlet bore 56 which directly
communicates with the rail line for receiving fuel at the common
rail pressure maintained by the accumulator. A threaded surface 58
surrounds the outer end of the inlet to receive a fitting to secure
the high pressure connection with the rail line 28. A first stage,
three-way valve 60 is controlled by a solenoid 62. Trim orifice 64
connects inlet bore 56 with valve 60. A threaded surface 68
surrounds the return bore for receiving a fitting to connect with
the return line 29. The valve 60 also implements selective
communication between the inlet bore 56 and an axial conduit 69
which supplies rail pressure to a second stage valve 70. The second
stage valve 70 controls the piston assembly 40 by filling and
spilling fuel, as will be described in detail below. The valve 60
may also be configured to close fluid communication with the rail
line and the return line.
The piston assembly 40 includes an intensifier piston 42, a control
piston 44 and a pump piston 46 coupled to the control piston 44. A
diagonal passage 41 communicates directly with the top of an
intensifier chamber 43 above the intensifier piston. The control
piston reciprocates in a control chamber 45 which communicates via
the second stage valve 70 and the first stage valve 60 with the
rail line. A pump chamber 47 disposed below the pump piston 46
communicates with the axial conduit 92.
The nozzle valve unit can be a conventional nozzle valve
configuration or it can be configured for a specific engine. As
illustrated, the nozzle valve unit 36 comprises an elongated valve
80 having an enlarged head 82 and a stem 84 which is slidably
received by an inwardly protruding fitting. The stem 84 terminates
in a tip 85. The tip 85 engages an interior conical seat 86 in the
nozzle. A spring 81 above the head biases the valve to a closed
position against the seat to prevent fluid from flowing through one
or more orifices 88 at the tip of the nozzle. Hydraulic pressure in
chamber 89 above the head may be used to assist in the valve
closure. Rail pressure can be applied to the nozzle valve spring
chamber 89 to make the nozzle opening pressure variable.
A valve chamber 90 surrounds an underside portion of the nozzle
head 82. The chamber communicates via a passage 92 with the pump
chamber 47. A fluid passage extends to the nozzle valve tip to
provide fluid communication to the interior lower portion of the
nozzle.
The diameters of the pistons of the piston assembly 40 may be
selected to provide for an intensifier piston function. In one
embodiment, the intensifier piston 42 has a diameter of 6.4
millimeters, the control piston 44 has a diameter of 8.0
millimeters and the pump piston 46 has a diameter of 4.5
millimeters. During filling, the piston assembly has a slight force
imbalance and lifts slowly while being controlled by the relatively
large trim orifice. When the position of pistons 42, 44 and 46
reaches a pre-established height, the pressure is vented by the
solenoid valve 50 to produce a large unbalanced force on the
intensifier assembly. The pistons of the piston assembly move
rapidly in a coordinated pump stroke to force intensified
pressurized fluid in the pump chamber 47 to the nozzle chamber 90.
The increased pressure in the nozzle chamber forces the valve 80 to
lift from its valve seat to inject pressurized fuel through the
nozzle orifice 88 into the cylinder of the engine. The pump plunger
has a spill port 49 which ensures a sharp end of the pumping
stroke. Flats 87 are formed on the cylindrical components
surrounding pistons 42, 44 and 46 to form a fuel return flow path
to return fuel to the tank. (See FIG. 3.) It should be noted that
the pressures required to produce movement of the piston assembly
are almost the same. A relatively large trim orifice produces the
pressure difference so that there are no large pressure drops and
very little energy is dissipated and relatively little waste heat
is generated.
The rate shape of a representative injection for one embodiment of
injector 10 is illustrated in FIG. 9. The graph shows the rate of
injection at 4,000 equivalent rpm as a function of the time in
seconds after the initial opening of valve 50 for various diameters
of rail inlet bore 56 at a constant length of 6.0 cm. The length
and diameter of inlet bore 56 have an effect on the initial
injection rate.
With reference to FIG. 4, a pilot control assembly 100 can also be
mounted within the nozzle body. The pilot control assembly employs
a pilot piston 102 which controls a ball valve 104. A spring 106
biases the valve to a closed position which prevents fluid
communication through a bleed passage which leads from passage 92.
The opening pressure of the ball valve defined by spring 106 is
greater than the nozzle opening pressure. A check valve 108 is
disposed at the bottom of the pump chamber. After the start of
injection, the pressure will rise to a level which causes the ball
to lift from its seat. The injection pressure which is exerted
against the larger diameter piston 102 will cause the piston to
lift very rapidly. The rapid lifting will displace a fixed quantity
of pressurized fuel from the fuel duct which will thus drop the
pressure in chamber 90 and bias the needle valve 80 toward the
closed position. However, the higher pumping rate will quickly
re-establish the pressure, and the valve 80 will again open. The
spill ending of the pump stroke via port 49 allows the pilot piston
to reset without pumping the fuel out of the orifice 88 to thereby
impose a pilot injection, such as illustrated in FIG. 10.
FIG. 10 illustrates representative pilot injection characteristics
for a pilot control assembly for various fuel supply conditions for
pump chamber 47. The graphical representations illustrate injected
fuel quantity, flow rate and nozzle end pressure through nozzle
88.
A number of additional embodiments of the common rail injector,
such as illustrated in FIGS. 5-8, are possible depending on the
sophistication and requirements of the operating characteristics
and the complexity of the nozzle construction. Each of the
embodiments controls the quantity of fuel injection by controlling
the fill time between injection events, e.g. the lifting of pistons
42, 44 and 46. The embodiments employ solenoid operated valves to
control the fill time. Pressure intensifiers having an efficient
construction and reliable operation are also advantageously
incorporated into the injector.
With reference to FIG. 5, an injector which incorporates a single
stage, one-way valve configuration is designated generally by the
numeral 110. The operation is governed by the status of a one-way
solenoid control valve 150. At a time after the last injection, the
valve 150 is open which thereby vents the control chamber 45 via
vent passage 152. Some of the rail fuel is lost through the control
orifice 154. The intensifier piston 42, control piston 44 and pump
piston 46 are displaced to the extreme bottom position of their
strokes. When the control valve 150 closes, the flow fills the
volume in the control chamber 45 via orifice 154. Low pressure is
applied to the pump chamber 47 at the bottom of the pump piston
through the check valve 160. The intensifier piston 42, control
piston 44 and pump piston 46 start to lift relatively slowly.
When it is time for the next injection event, valve 150 reopens
pursuant to a command from the electronic control 30. The pressure
in the control chamber 45 below the control piston therefore drops,
and the intensifier piston, control piston and pump piston are
displaced downwardly in a very rapid fashion. The volume of fuel in
the pump chamber 47 below the pump piston is forced via passage 164
into the nozzle chamber 90 which lifts the nozzle valve 80 to
inject pressurized fuel through orifice 88. The injection ends when
the spill port 49 comes into alignment or when the control piston
44 hits its stop. For injector 110, the injected fuel quantity is
controlled by the amount of time available for filling the control
chamber 45. For maximum fuel quantity, filling starts soon after
the last injection. For very small fuel quantity, filling starts
just before the start of the next injection. The filling is
precisely controlled by the solenoid control valve 150.
With reference to FIG. 6, a common rail injector implementing a
single stage, three-way valve configuration is shown generally as
injector 210. For injector 210, sometime after the last injection,
valve 250 is open thereby venting the control chamber 45 via
passage 252. The intensifier piston 42, control piston 44 and pump
piston 46 are displaced to the bottom of their strokes. The
solenoid control activates valve 250 to close, thereby supplying
fuel via passage 254 to the control chamber 45 below the control
piston 44. Low pressure fuel is supplied to the pump chamber 47
below the pump piston through the check valve 260. A passage 264
also communicates to the nozzle chamber 90.
Upon closing of valve 250, the intensifier piston 42, control
piston 44 and pump piston 46 start to lift in a relatively slow
manner. A command is transmitted to the solenoid to open valve 250
and vent the pressure via vent passage 252. The pressure in the
control chamber 45 decreases. The intensifier piston, control
piston and pump piston travel downwardly in a very rapid fashion to
force the volume of fuel below the pump piston from the pump
chamber 47 into the nozzle chamber 90. The pressure in chamber 90
forces the nozzle valve 80 to lift and inject pressurized fuel
through orifice 88. The fuel injection ends when the spill port 49
comes into alignment or the control piston 44 hits its stop. For
this injector 210, the fuel quantity is again controlled by the
amount of time available for filling. For example, for maximum fuel
quantity, filling starts very soon after the last injection. For
very small fuel quantity, filling starts just before the start of
the next injection.
With reference to FIG. 7, a common rail injector implementing a two
stage, one-way injection is designated by the numeral 310. After an
injection event, valve 340 is in the open position. Some of the
rail pressure flows through orifice 342 out to return through valve
340. Valve 350 is open venting the bottom of the control chamber 45
through vent passage 352. The intensifier piston, control piston
and pump piston are at the bottom of their pump strokes.
A command from the electronic control 30 closes valve 340 to
thereby allow pressure to build up on the back side of valve 350.
Valve 350 closes. The pressure is applied to the bottom of the
control piston through the passage 351 in the valve. Low pressure
is supplied to the pump chamber 47 at the bottom of the pump piston
46 through the check valve 360. The intensifier piston, control
piston and pump piston start to lift in a slow fashion. When it is
time for the next injection event, valve 340 is activated to the
open position. The pressure above valve 350 drops, valve 350 opens
and the pressure below the control piston 44 therefore drops. The
intensifier piston, control piston and pump piston travel
downwardly in very rapid fashion, and the volume of fuel below the
pump piston is forced into the nozzle chamber 90 to lift the valve
80 and inject pressurized fuel through the nozzle orifice 88. The
injection ends when the spill port 49 comes into alignment or the
control piston 44 hits the stop. The fuel quantity is again
controlled by the amount of time available for filling.
With reference to FIG. 8, a common rail injector implementing a two
stage, three-way valve configuration is designated by the numeral
410. Starting at sometime after the last injection event, the
solenoid valve 440 is open to low pressure. Valve 450 is open,
thereby venting the control chamber 45 via vent passage 452. The
intensifier piston, control piston and pump piston are at the
bottom of their strokes. Valve 440 then switches to a second
position to supply pressure to the back side of valve 450. Valve
450 then closes. Pressure is supplied to the control chamber 45
below the control piston through the passage 451 in the valve 450.
Low pressure is also supplied to the pump chamber below the pump
piston through the check valve 460. The intensifier piston, control
piston and pump piston start to lift in a slow fashion. When it is
time for the next injection event, valve 440 switches to a third
position. The pressure above valve 450 decreases, valve 450 moves
and the pressure below the control piston in the piston chamber
decreases. The intensifier piston, control piston and pump piston
travel downwardly in very rapid fashion. The volume of fuel below
the pump piston is then injected until the spill port 49 opens or
the control piston hits its stop. Again, the fuel quantity is
controlled by the amount of time available for filling.
It will be appreciated that for each of the foregoing common rail
injectors, the nozzle is filled between injections. The end of the
filling is essentially the start of the next injection, but the
filling period is significantly longer than the injection
period--typically, approximately ten times as much longer. Because
of the foregoing characteristics, the fuel quantity is much less
sensitive to the valve timing compared to other nozzles that use
the control valve to start and stop the injection directly. In
addition, the solenoid opens and closes the control valve when
conditions are more quiescent. If the intensifier piston 42 and the
pump piston 46 are substantially the same diameter, the injection
pressure is equal to the rail pressure. However, if the intensifier
piston is larger than the pump piston, the injection pressure will
be higher than rail pressure.
The common rail injectors as described are operable so that the
injected fuel is introduced at a relatively slow rate and in an
accurate fashion between injection events and then is injected
rapidly and at a high pressure during injection. The pistons are
substantially balanced during the filling process. Consequently,
there is a small pressure drop and small energy loss as a result of
the filling process. In addition, the injector configuration allows
for the incorporation of a trim orifice of relatively large
diameter. Such a trim orifice configuration is relatively easy to
manufacture and is not sensitive to small amounts of wear during
operation.
For common rail injector configurations as described, the rail
pressure does not act on the valve tip between injection events.
Consequently, even if the valve tip were leaky, such a condition
would not result in the engine being greatly overfueled. For the
common rail injectors, the maximum fuel delivery is limited by the
piston stroke. Thus, no failure mode can cause a single injection
to exceed the maximum allowable fuel quantity designed into the
piston assembly. Repeated or continuous injection commands cannot
produce unlimited fuel quantities because the control piston must
be refilled for each injection event.
While a number of embodiments have been set forth for purposes of
describing the invention, the foregoing descriptions are not a
limitation of the invention. Accordingly, various modifications,
adaptations and alternatives may also occur to one skilled in the
art without departing from the spirit and the scope of the present
invention.
* * * * *